The large number of vehicles operating on the roads cause high emissions and consequently a negative effect on the environment. When developing and optimizing internal combustion engines, certain requirements must be considered, which are environmental regulations, reduced fuel consumption and increased specific power. In order to meet these demands, an increase of the engine combustion pressure will occur usually accompanied with a temperature increase. During start-up and shut-down of an engine, it is subjected to cyclic thermo-mechanical fatigue (TMF) loads. The turbo manifold and exhaust manifolds connected to the engine is also subjected to these thermo-mechanical fatigue loads and thereby exposed to alternating tensile and compression loads. As these TMF loads will increase in the near future due to the development and optimization of internal combustion engines, it is important to understand the limitations of the material for these loads. In collaboration with Scania CV AB in Södertälje, this thesis covers the investigation of influence of nitrocarburizing (NC) on TMF properties of three ductile irons (DCI) labelled HiSi, SiMo51 and SiMo1000 intended to be used for components in the exhaust system. Nitrocarburizing is a thermo-chemical process where nitrogen and carbon diffuses from the process medium into the surface zone of a ferrous metal. The purpose of the NC is to increase the wear properties in contact areas between different parts. The oxidation with and without nitrocarburizing are studied both after isothermal and stress free oxidation tests at 780 °C and after TMF loads with combined cyclic variation of mechanical and thermal loads. In addition, the properties such as hardness, defects, porosity, microstructure, composition of both the materials and of the oxide layer have been investigated. For SiMo1000+NC cracks formed during nitrocarburizing were positioned parallel to the surface edge in the diffusion zone and consequently an increased diffusion of nitrogen into the material, i.e. deeper diffusion depth. SiMo1000+NC showed highest hardness, highest compressive residual stresses and thickest oxide layer. SiMo1000 showed highest resistance against oxidation due to the protective aluminum oxide layer. Oxide crack initiations after thermo-mechanical tests with a protective silicon oxide layer around the cracks for HiSi and SiMo51 and a protective aluminum oxide layer around the cracks for SiMo1000. In materials with nitrocarburizing, these protective layers of either silicon oxide or aluminum oxide were more distributed into the material. In SiMo1000+NC, crack initiations were not oxidized.

Traditionally, geothermal boreholes have utilized the ground energy for space heating and cooling. In this system, a circulation loop is placed in a small-diameter borehole typically extending to a depth of 200-300 ft. The hole is then backfilled with a mixture of sand, bentonite and/or cement. The loop is connected to a geothermal heat pump and the fluid inside the loop is circulated. The heat energy is fed into the ground for cooling in the summer and withdrawn from the ground for heating in the winter. Geothermal heat pumps work more efficiently for space heating and cooling compared to air-source heat pumps.  The reason is ground-source systems use the ground as a constant temperature source which serves as a more favorable baseline compared to the ambient air temperature. A significant cost associated with any deep geothermal borehole is the drilling required for installation. Because Energy Piles perform the dual function of exchanging heat and providing structural support, and are only installed at sites where pile foundations are already required, these systems provide the thermal performance of deep geothermal systems without the additional drilling costs. Low maintenance, long lifetime, less variation in energy supply compared to solar and wind power, and environmental friendliness have been cited as additional Energy Pile advantages. Case studies show that they can significantly lower heating/cooling costs and reduce the carbon footprint. Energy cost savings for typical buildings outfitted with Energy Piles could be as much as 70 percent. The use of Energy Piles has rapidly increased over the last decade, especially in Europe where more than 500 applications are reported. Primary installations have been in Germany, Austria, Switzerland and United Kingdom. Notable projects include the 56-story high Frankfurt Main Tower in Germany, Dock E Terminal Extension at Zurich International Airport in Switzerland and the One New Change building complex in London U.K. Energy piles have seen very little use in the North America, only a handful of completed projects are known; Marine Discovery Center in Ontario, Canada, Lakefront Hotel in Geneva, New York and the Art Stable building in Seattle, Washington. Energy Piles are typically installed with cast-in-place technology (i.e. drilled shafts, continuous flight auger piles, micropiles etc.) while some driven pile applications are also reported. Other types of geotechnical structures in contact with the ground, such as shallow foundations, retaining walls, basement walls, tunnel linings and earth anchors, also offer significant potential for harnessing near-surface geothermal energy. Energy Pile design needs to integrate geotechnical, structural and heat exchange considerations. Geotechnical characteristics of the foundation soils and the level of the structural loads are typically the deciding factors for the selection and dimensioning of the pile foundations. The geothermal heat exchange capacity of an Energy Pile is a key parameter to be considered in design. Thermal characteristics of the ground as well as the heating and cooling loads from the structure need to be considered for the number of piles that will be utilized as heat exchangers. Therefore, the thermal properties of the site need to be evaluated for an Energy Pile application in addition to the traditional geotechnical characterization for foundation design. Energy Piles bring new challenges to geotechnical pile design. During a heat exchange operation, the pile will expand and contract relative to the soil as heat is injected and extracted, respectively. These relative movements have the potential to alter the shear transfer mechanism at the pile-soil interface.  Furthermore, the range of temperature increases near the pile surface, though limited by practical operational guidelines, can have a significant effect on pore pressures generation and soil strength. This dissertation provides answers for several research questions including the long-term performance of Energy Piles, the applicability of the thermal conductivity tests to Energy Piles.  Furthermore, it presents the results and a detailed discussion about the full scale in-situ thermo-mechanical pile load test conducted at Virginia Tech. / Ph. D.

Hallsta Paper Mill, which is a part of Holmen Paper, uses the Thermo Mechanical Pulping process to produce paper pulp. One of their process steps is a plug screw feeder that transport and compresses chips. Jams often occur in the plug screw and there is currently a lack of knowledge of how it should be operated for the highest possible production quantity. The purpose of the thesis is to identify the causes that lead to failures of the plug screw and to find an optimal way of operating it.  In order to gain a deeper understanding of the different areas covered by the study, the theory of the Thermo Mechanical Pulping process used at Holmen for production of paper pulp has been presented. Also, theory about how the chips is being processed, the plug screw and its dimensions, the improvement strategy used in the study and about maintenance.  Collecting documents was done using business systems such as IFS and WinMops and interviews were conducted. The data analysis method used were a regression analysis and a fishbone diagram. From this, optimal parameters for operating the plug screw have been developed.  From the results, an improvement proposal has been designed to create clear guidelines for operating and maintaining the screw as well as other production steps that have an impact on the screw, in order to avoid unnecessary wear and failures of the plug screw.

Structural elements comprised of high strength concrete (HSCs) have gained popularity due to their high compressive strength, increased tensile strength, and low permeability that can be achieved with smaller placements relative to what would be needed with traditional ready mixed concretes. HSCs are also gaining interest for mass placements that are very large. Determining in-place properties of any of these structures is critical to the overall success of a project and elusive to determine prior to placement. In this dissertation, a laboratory based thermo-mechanical framework is outlined to predict in-place properties of modest to mass sized HSC structures using mostly existing and common laboratory testing methods with a few additional items on the same scale as existing equipment. Various curing protocols were evaluated in this study to determine a recommended set of protocols to reproduce thermal profiles of modest and mass sized structures on laboratory scale specimens. These specimens can then be tested following standard testing protocols to reasonably estimate in-place mechanical properties. This framework is envisioned to be a foundational piece of a standard test method in the future. Approximately 600 concrete specimens were tested for compressive strength, 300 specimens for elastic modulus, 100 for splitting tensile strength as well as 100 cement paste specimens for compressive strength. Additionally, approximately 400 time-temperature curves were recorded for both cement paste and HSC specimens.

No description available.

The goal of more efficiently and more reliably realizing energy conversion in the power electronics industry is pushing the limits of current wire bonding packaging technology. Emerging three-dimensional power packaging techniques have shown their potential to replace wire bonding technology down the road. However, these innovative technologies have not yet been fully understood in terms of thermal and thermo-mechanical performance. Therefore, a comparative evaluation between the thermally induced response in conventional wire bonding (a 2-Dimensional technology) and 3-Dimensional packaging technologies is essential. Thermal and thermo-mechanical analysis using the Finite Element Method (FEM) has been performed to evaluate a three-dimensional power module packaged in a Metal Post Interconnected-Parallel Plate Structure (the MPIPPS), and the result is compared with that of a wire bond module. Under the same single-sided cooling conditions, thermal modeling results show a significantly lower junction temperature of 17oC in the MPIPPS module than that in the wire bond module, due to the more uniform heat flow distribution in the MPIPPS module. The top DBC (direct bonded copper) substrate in the MPIPPS module helps direct the excessive heat generated from IGBT (Insulated Gate Bipolar Transistor) chips to diode chips (which dissipates less heat). The maximum junction temperature is reduced to 108 oC in the MPIPPS module by the implementation of double-sided cooling, which the wire bonding technique can not achieve. Subsequent thermo-mechanical analysis reveals the weak points in both modules during temperature cycling and power cycling. In the wire bond module, temperature cycle results have shown more severe stress and strain than that those of the power cycling conditions in the regions where the wires attach the device emitter pads. In the MPIPPS module, the solder joints exhibit high plastic and creep deformation. Power cycling produces more inelastic deformation at the solder joints between the posts and device, due to local over-heating, which causes more severe high-temperature creep deformation. Using a deformation-based thermal fatigue theory, the solder joint fatigue lives are predicted. Compared with the commercial wire bond module temperature cycle test, the fatigue life of MPIPPS is limited. We conclude that the MPIPPS module is better in thermal management but is thermo-mechanically less reliable than the wire bond module. / Master of Science

This study mainly evaluated the thermo-mechanical reliability of lead-free packaging techniques for attaching large-area chip. With 3 MPa pressure, a low-temperature (<300oC) sintering technique enabled by a nano-scale silver paste was developed for attaching 100 mm2 silicon die. This new lead-free packaging technique for die-attachment was compared with soldering by vacuum reflow. Lead-free solder SAC305 and SN100C were selected and used in this work since they were widely used in electronic packaging industry. Inspection of as-prepared die-attachments by X-ray and optical microscopy (observation of cross-section) showed that the voids percentage in solder joint was less than 5% and no voids was observed at the scale of hundreds of micron in sintered silver joint. Then these die-attachment were thermal cycled with the temperature range from -40oC to 125oC. Deduction of curvature and residual stresses were found for both soldered and sintered die-attachment. After 800 cycles, the residual stresses in silicon-solder-copper sample already decreased to around 0. The SEM images of solder and silver joint after 800 thermal cycles showed that cracks longer than 2.5 mm already grew in both kinds of solder joint (die-attachment of Si-Solder-Copper). In contrast, no cracks or voids at the scale of hundreds of micron were defected in silver joint. Based on these observation, different mode of stress-relaxation were proposed for sintered silver and solder, respectively. While solder joint released stresses by crack growth, the silver joint relied on the deformation of porous structure, and plastic deformation may occur. The pressure-sintering process with double printing and drying was proved to be a reliable process to produce sintered - silver bonding with high strength. The reliability of silver joint was better than that of SAC305 or SN100C. Besides, the technique of measuring the curvature by laser scanning, introduced in this work, showed its significance by directly reflecting the bonding integrity of die-attachment. As a nondestructive testing technique, It was a cheaper and faster way to examine the die-attachment. Additionally, it overcame the disadvantage of X-ray Inspection: it was of the ability to differentiate between layers of die-attachment. / Master of Science

New stricter environmental legislation requires lower emissions and fuel consumption of automotive engines. Therefore the fuel efficiency must be increased but this leads to higher loads in the engine. As for the exhaust system it is affected by higher thermomechanical loads. Until today the turbo manifold has been nitrocarburized in order to increase the wear resistance in slip joints with other exhaust components. The problem is that there is no knowledge of how the nitrocarburizing affects the thermomechanical properties of the material. The purpose of this thesis work is to examine the difference in thermomechanical properties with and without nitrocarburizing on the three different ductile irons High Silicon, SiMo51 and SiMo1000 intended for exhaust components. Thermo-mechanical fatigue (TMF) experiments were performed on test rods to evaluate difference in number of cycles to failure. In each cycle the test-rod was affected by a combination of mechanical loads and thermal loads resembling those found on exhaust components. Light optical microscopy, scanning electron microscopy and x-ray radiography were used to examine microcracks and damage mechanisms of the materials. It was found that the nitrocarburizing did not affect the number of cycles to failure in any large extent. Further, it was also found that SiMo1000 on average has the longest lifetime followed by SiMo51 and High Silicon. Although, the difference is small for many loadings and taking a 95% confidence band into account the curves overlap for many loading cases.

In order to investigate the thermal stress and expansion as well as the associated strain effect on material properties caused by high temperature and large temperature gradient, a two-way thermo-mechanical coupling solver is developed. This solver integrates a new structural response module to the Kentucky Aerothermodynamics and Thermal response System (KATS) framework. The structural solver uses a finite volume approach to solve either hyperbolic equations for transient solid mechanics, or elliptic equations for static solid mechanics. Then, based on the same framework, a quasi-static approach is used to couple the structural response and thermal response to estimate the thermal expansion and stress within Thermal Protection System (TPS) materials. To better capture the thermal expansion and study its impacts on material properties such as conductivity and porosity, a moving mesh scheme is also developed and incorporated into the solver. Grid deformation is transferred among different modules in the form of variations of geometric parameters and strain effects. By doing so, a bi-direction information loop is formed to accomplish the two-way strong thermo-mechanical coupling. Results revealed that the thermal stress experienced during atmospheric re-entry concentrates in a banded area at the edge of the pyrolysis zone and its magnitude can be large enough to cause the failure of the TPS. In addition, thermal expansion causes the whole structure to deform and the changes in material properties. Results also indicated that the impacts coming from structural response should not be ignored in thermal response.

Thermomechanical pulping (TMP) is a highly energy intensive process where most of the energy is used in therefining of chips to fibres. Various ways of reducing the energy consumption have earlier been studied, for examplechange of refiner pattern, addition of various chemicals, and also some biochemical implementation in the form of fungus and enzymes. This study includes pre-trials with the enzymes pectin lyase and pectin esterase,multipectinase, xylanase, and mannanase. The results are studied via a reducing sugar assay, an enzymatic assayusing spectrophotometry, and capillary zone electrophoresis. The study also includes results from a pilot scalerefining with multipectinase, xylanase, and mannanase, performed with a wing refiner at Helsinki University.Reductions of energy consumption in TMP by pre-treatment of Norwegian spruce chips are investigated and apotential reduction of energy consumption of 6 % is indicated.